Rho kinase (ROCK) is a member of the serine-threonine protein kinase family. ROCK exists in two isoforms, ROCK1 and ROCK2. ROCK has been identified as an effector molecule of RhoA, a small GTP-binding protein (G protein) that plays a key role in multiple cellular signaling pathways. ROCK and RhoA are ubiquitously expressed across tissues. The RhoA/ROCK signaling pathway is involved in a number of cellular functions, such as actin organization, cell adhesion, cell migration, and cytokinesis. It is also directly involved in regulating smooth muscle contraction. Upon activation of its receptor, RhoA is activated, and, in turn, it activates ROCK. Activated ROCK phosphorylates the myosin-binding subunit of myosin light chain phosphatase, which inhibits activity of the phosphatase and leads to contraction. Contraction of the smooth muscle in the vasculature increases blood pressure, leading to hypertension.
There is considerable evidence in the literature that the RhoA/ROCK signaling pathway plays an important role in signal transduction initiated by several vasoactive factors, for example angiotensin II, urotension II, endothelin-1, serotonin, norepinephrine and platelet-derived growth factor (PDGF). Many of these factors are implicated in the pathogenesis of cardiovascular disease.
Additional studies in the literature, some using the known ROCK inhibitors fasudil or Y-27632 further illustrate the link between ROCK and cardiovascular disease. For example, ROCK expression and activity have been shown to be elevated in spontaneously hypertensive rats, suggesting a link to the development of hypertension in these animals. The ROCK inhibitor Y-27632 was shown to significantly decrease blood pressure in three rat models of hypertension, including the spontaneously hypertensive rat, renal hypertensive rat and deoxycortisone acetate salt hypertensive rat models, while having only a minor effect on blood pressure in control rats. This reinforces the link between ROCK and hypertension.
Other studies suggest a link between ROCK and atherosclerosis. For example, gene transfer of a dominant negative form of ROCK suppressed neointimal formation following balloon injury in porcine femoral arteries. In a similar model, ROCK inhibitor Y-27632 also inhibited neointimal formation in rats. In a porcine model of IL-1 beta-induced coronary stenosis, long term treatment with the ROCK inhibitor fasudil was shown to progressively reduce coronary stenosis, as well as promote a regression of coronary constrictive remodeling.
Additional investigations suggest that a ROCK inhibitor would be useful in treating other cardiovascular diseases. For example, in a rat stroke model, fasudil was shown to reduce both the infarct size and neurologic deficit. The ROCK inhibitor Y-27632 was shown to improve ventricular hypertrophy and function in a model of congestive heart failure in Dahl salt-sensitive rats.
Other animal or clinical studies have implicated ROCK in additional diseases including coronary vasospasm, cerebral vasospasm, ischemia/reperfusion injury, pulmonary hypertension, angina, renal disease and erectile dysfunction.
In another study, it has been demonstrated that inhibition of the RhoA/ROCK signaling pathway allows formation of multiple competing lamellipodia that disrupt the productive migration of monocytes. It has also been reported that small molecule inhibitors of Rho kinase are capable of inhibiting MCP-1 mediated chemotaxis in vitro. Due to the dependence of immune cell migration upon the RhoA/ROCK signaling pathway one would anticipate inhibition of Rho kinase should also provide benefit for diseases such as rheumatoid arthritis, psoriasis, and inflammatory bowel disease.
The above studies provide evidence for a link between ROCK and cardiovascular diseases including hypertension, atherosclerosis, restenosis, stroke, heart failure, coronary vasospasm, cerebral vasospasm, ischemia/reperfusion injury, pulmonary hypertension and angina, as well as renal disease and erectile dysfunction. Given the demonstrated effect of ROCK on smooth muscle, ROCK inhibitors may also be useful in other diseases involving smooth muscle hyper-reactivity, including asthma and glaucoma. Furthermore, Rho kinase has been indicated as a drug target for the treatment of various other diseases, including airway inflammation and hyperresponsiveness, cancer, as well as neurological disorders, such as spinal-cord injury, Alzheimer disease, multiple sclerosis, stroke and neuropathic pain.
There remains an unmet medical need for new drugs to treat cardiovascular disease. A study published in 2003 estimated that almost 29% of the adult U.S. population had hypertension in 1999-2000 (I. Hajjar et al., JAMA, 2003, 290, 199-206). Furthermore, 69% of the hypertensive individuals studied during this period did not have their hypertension controlled at the time their blood pressure was measured. This figure was worse in patients with diabetes and hypertension where 75% of those patients studied did not have their blood pressure controlled to the target level. Another more recent study showed similar results, with less than one-third of hypertensive patients studied having blood pressure controlled to the target level (V. Andros, Am. J. Manag. Care, 2005, 11, S215-S219). Therefore, despite the number of medications available to treat hypertension, including diuretics, beta blockers, angiotensin converting enzyme inhibitors, angiotensin blockers and calcium channel blockers, hypertension remains poorly controlled or resistant to current medication for many patients. If not adequately treated, hypertension can lead to other cardiovascular diseases and organ failure including coronary artery disease, stroke, myocardial infarction, cardiac failure, renal failure and peripheral artery disease.
Although there are many reports of ROCK inhibitors under investigation, fasudil is the only marketed ROCK inhibitor at this time. An i.v. formulation was approved in Japan for treatment of cerebral vasospasm. There remains a need for new therapeutics, including ROCK inhibitors, for the treatment of cardiovascular diseases, cancer, neurological diseases, renal diseases, bronchial asthma, erectile dysfunction, and glaucoma.